OXIDATION-KINETICS OF SIC DEPOSITED FROM CH3SICL3/H2 UNDER CVI CONDITIONS

Oxidation tests were performed on SiC deposits prepared from CH3SiCl3/H-2 under chemical vapour infiltration conditions, at temperatures ranging from 900-1500-degrees-C under a flow of pure oxygen at 100 kPa (passive oxidation regime). The kinetics of growth of the silica layer were established from thickness measurements performed by spectroreflectometry. They obey classical parabolic laws from which rate constants are calculated. Within 1000-1400-degrees-C, the oxidation process is thermally activated with an apparent activation energy of 128 kJ mol-1. Above 1400-degrees-C and below 1000-degrees-C, an increase in the activation energy is observed which is thought to be related to a change in the mechanism of the oxygen transport across the silica layer for T > 1400-degrees-C and tentatively to stress effects for T < 1000-degrees-C. The kinetics data are compared to those measured on silicon single crystals (used as a standard) and to other reported data on SiC.